This invention relate""s to a method of forming a brush seal between two relatively movable components. The invention further relates to a brush seal when formed by the method, and a machine having such a brush seal.
Brush seals are widely used in the rotating machinery art, to effect seals particularly in gas turbines, jet engines and other circumstances where there is one component which rotates at a relatively high rotational rate with respect to another component, and where there are arduous operating conditions such as high temperatures, corrosive gases and high pressures. A typical gas turbine or jet engine has a housing in which is rotatably mounted a rotor. A brush seal arranged to effect a seal between the housing and the rotor may have an annular carrier plate adapted to be mounted on the housing so as to surround with clearance the rotor shaft. The radially outer part of the carrier plate has a plurality of inwardly projecting bristles secured thereto, the length of the bristles being accurately finished so that the free bristle tips lightly wipe on the surface of the rotor shaft. The carrier plate should be mounted so that it is on the low pressure side of the seal and thus supports the bristles except for the tips of the bristles projecting beyond the carrier plate.
There have been proposed many improvements to the basic design of brush seal discussed above. One particular area which has been addressed is the need to undertake major dismantling of the machine in the event that a worn or damaged brush seal is to be replaced by a new seal. For example, it is known to provide the carrier in two or more arcuate pieces which accurately interfit and each of which supports a respective segment of the complete brush seal, so that when pieces of the carrier are all assembled to the housing of the machine, a continuous brush seal is formed around the shaft. When the seal is to be replaced, it may be removed in pieces without the need wholly to dismantle the machine.
More recently, it has been proposed to provide a carrier in annular pieces and having a T-shaped circumferential slot, for use with a flexible brush seal element having a T-shaped head at its radially outer end and which fits into the slot in the housing. When the seal is to be replaced, the old seal element may be slid out of the slot and a new element then fed into the slot. Support for the bristles is provided by the wall in the carrier on the low pressure side of the seal assembly and which defines the slot. Such a seal is both cheaper to produce and easier to fit but does still require some disassembly of the housing, since the carrier unit must be removed in one piece before it can be separated to give access to an end of the slot, to permit removal of the old brush seal element in insertion of the new element.
Another brush seal arrangement is shown in EP-0905421-A, where the fixing procedure for the seal element uses a member pressed into a slot within which the seal element is located. In order to guarantee the final position of the seal element, the bristles are held in a carrier which then locates against shoulders formed in a backing plate and the pressed-in fixing member, and in these components lock into a specially-formed slot in the housing. These complexities lead to significantly higher manufacturing costs for the housing, the brush seal element and the associated backing plate and fixing member.
The present invention aims at providing an improved method of assembling a brush seal between two relatively moveable components, which method uses a flexible brush seal element, and which permits easy and rapid replacement of the seal in the event that the seal becomes worn or damaged.
Accordingly, one aspect of the present invention provides a method of forming a brush seal between two relatively moveable components having confronting adjacent surfaces, comprising:
providing a flexible brush seal element comprising a plurality of metallic bristles arranged side by side and having their one ends fused together to form an elongate strip, the fused ends being turned to project laterally from the general plane of the elongate strip and the other ends of the bristles being substantially in alignment;
providing a slot in one of the components which slot opens into said surface of the one component to face the confronting surface of the other component, the width of the slot being greater than the thickness of the brush seal element in the region of the bristles thereof;
pushing the fused end of the brush seal element into the slot so that the other ends of the bristles project from said surface of the one component; and then
pressing an anchoring strip into the slot which strip which bears on a wall of the slot and on the brush seal element to trap the laterally-projecting fused one ends of the bristles within the slot, so securing the brush seal element in defined position.
Though the method of this invention is primarily intended to effect a seal between relatively rotatable components, such as the rotor of a gas turbine or jet engine and a housing therefor, the method may be used to form a brush seal between other components. For example, a seal may be formed by the method between two generally planar components or even between two irregularly shaped components. However, in the following the invention will mainly be described with reference to the principal intended use, but the invention is not to be regarded as limited to that use.
It will be appreciated that by the method of the present invention, a brush seal may be fitted to a housing so long as there is access to the surface of the housing which faces the moving component to which a seal is to be made. Though generally the slot would be formed in a carrier bolted or otherwise suitably affixed to the main engine housing, in fact the slot could be formed directly in the housing of the engine or other machine. Since access is not required to a circumferential end of the slot, for most installations, it will be sufficient to remove the shaft from the housing, or to move that part of the housing in which the seal is to be installed away from the shaft, which ever is the most convenient. The removal of the worn or damaged seal is performed by pulling out of the slot the projecting parts of the bristles and though this is likely to cause further damage to the seal element, this generally is not a problem since the seal ordinarily would be regarded as scrap, before removal.
The bristles making up the brush seal element could have their one ends (that is, for a xe2x80x9cconventionalxe2x80x9d gas turbine or jet engine brush seal, the radially outer ends of the bristles) fused together by a simple welding or brazing process. For example, the bristles could be suitably arranged in a clamping device holding the greater part of the length of the bristles but with their one ends exposed, the welding or brazing process then being performed on those exposed ends. The volume of filler material used during such a welding or brazing process may be controlled so that the shape and dimensions of the fused-together ends falls within certain predefined limits but giving the brush seal element an enlarged head at the one ends of the bristles, turned to project laterally from the general plane of the strip.
Another possibility for the manufacture of the brush seal element may include wrapping the bristles around a filler wire extending along the length of the brush seal element and then fusing the bristles to that filler wire. In this case, each bristle may be sufficiently long, prior to wrapping around the filler wire, to permit the two ends of each bristle to lie adjacent one another, when wrapped round the filler wire.
Following the fusing of the one ends of the bristles, that fused end of the brush seal element may be finished for example by a grinding or machining operation so as to give the fused end a predefined bead-like profile. Then, the length of the bristles should be accurately finished, again by a grinding or other operation on the free ends of the bristles, using the fused end as a reference surface.
The slot in the one component may be of simple rectangular cross-section, with the fused end of the brush seal element accommodated against the base wall of the slotxe2x80x94and in the typical application for a gas turbine, that base wall would be the radially outer end of the slot. In such a case, the anchoring strip should simply be pressed into the slot following the positioning of the seal element therein, the strip bearing on one face of the bristles of the element and on the opposed wall of the slot. The anchoring strip should be pressed fully home, so as to bear against the fused end of the brush seal element, forcing that part of the seal against the base wall of the slot, using a special tool which deforms the anchoring strip to ensure retention of the brush seal element in the slot and the sealing of the element thereto.
Another possibility includes the provision of a slot having an undercut portion at the base end of the slot, whereby the fused end of the flexible brush seal element may at least partially be accommodated in that undercut portion. In this way, distortion of the fused end of the seal by the insertion of the anchoring strip may be minimised.
The component in which the slot is formed may comprise a part of the overall housing of the rotary machine, or may comprise a separate carrier which is adapted to be secured to the housing. The latter arrangement is preferred, as the degree of dismantling to change a worn or damaged seal may be minimised; on releasing the carrier from the housing, the carrier may simply be slid axially off the rotor shaft to give access to the carrier bore for changing the seal element.
A support plate may be positioned between the anchoring strip and the brush seal element, which support plate serves to support the bristles on the side thereof remote from the wall of the housing engaged by the bristles. Such a support plate preferably extends for substantially the entire depth of the slot, so as to support the majority of the length of the bristles, whereby the free ends of the bristles may still perform the required sealing function.
In the case of a seal for use with a shaft which may rotate in either direction with respect to the component in which the seal is mounted, the bristles may extend strictly radially from the with respect to the shaft. The bristles may similarly project for a case where the two components move relative to one another in the plane of the confronting surfaces. If however a shaft always rotates in one sense, then the bristles may lie at an angle to the true radial direction, so as to perform a wiping action over the surface of the shaft. Such an arrangement permits easy deflection of the bristles should the shaft perform minor perturbations about its mean positionxe2x80x94for example, in the case of a gas turbine rotor which may normally run at many tens of thousands of rpm, the rotor may pass through periods of vibration as it runs up to normal speed. Other possibilities include providing a seal with two layers of bristles arranged with one layer overlying the other, but with the bristles of one layer at the opposite angle to that of the other layer, with respect to the true radial direction.
This invention extends to a brush seal assembly arranged to form a seal between two relatively movable components, whenever assembled by a method of this invention. Further, this invention also extends to a machine with two relatively moveable components whenever provided with a brush seal by a method of this invention, and to a machine having two relatively movable components and a brush seal assembly of this invention installed between those two components.